1. Field of the Invention
The present invention generally relates to lighting fixtures and luminaires, and more particularly to an improved light transmitting film for use with a light reflecting or light transmitting member of a lighting fixture.
2. Description of the Prior Art
As used herein, the term lighting fixture includes luminaires and indoor and outdoor lighting fixtures. Typically a lighting fixture includes a light source, a light reflecting member, such as, a reflector, and/or a light transmitting member, such as, a refractor, a lens, or an enclosure. The reflecting and/or transmitting members are to redirect or direct the light rays emitted from the light source. Due to the temperatures resulting from high power lamps, a high temperature resistant material, usually polycarbonate, glass or acrylic is used for the light reflecting and/or light transmitting members. However, none of the known materials provide both significant impact strength and resistance to degradation from ultraviolet (UV) radiation and heat. Glass lacks impact strength and is relatively easily cracked or shattered. Plastic materials become yellow over time under the effects of UV radiation received from the light source.
U.S. Pat. No. 3,284,625 issued to Barnes and assigned to the present assignee, discloses a disposable liner or insert for protecting a plastic light transmitting member from degradation from ultraviolet radiation. The liner conforms to the interior configuration of a globe or refractor of a lighting fixture and has sufficient thickness to be opaque to ultraviolet radiation from the light source which would otherwise yellow the wall of the outer light transmitting element. The liner itself becomes yellowed over time and is removed, disposed of and replaced by a new liner. In this way, a relatively simple, inexpensive improved structure is provided by the disposable liner. The insert is made of a film of plastic material, for example, such as by vacuum molding a film of polycarbonate material which begins at about 0.008" thick and provides a resulting liner having a thickness of 0.002-inch or 0.003-inch. Where the liner is made of an acrylic plastic material, a somewhat thicker wall thickness is required, for example of 0.010-inch or 0.012-inch.
U.S. Pat. No. 4,903,180 issued to Taylor et al. discloses a cover for protecting internal reflecting prisms formed on an outer surface of a reflector from deposits and contaminants from the surrounding atmosphere. The cover is vacuum formed from a 1/8-inch thick sheet of clear acrylic resin.
U.S. Pat. No. 4,380,794 discloses a surgical lamp including a reflector molded from polyetherimide resin and having a dichroic coating for reflecting visible light while passing infrared light.
It is desirable to provide a permanent improved light transmitting film for use with a light reflecting and/or light transmitting member for increasing the longevity of a lighting fixture, and that does not, itself, require periodic replacement. It is further desirable to provide such an improved light transmitting film that achieves the required lumen output substantially without negative effect.